The ADC field includes a variety of different types of ADC data carriers and ADC readers operable to read data encoded in such data carriers. For example, data may be encoded in machine-readable symbols, such as barcode symbols, area or matrix code symbols, and/or stack code symbols. Machine-readable symbols readers may employ a scanner and/or imager to capture the data encoded in the optical pattern of such machine-readable symbols. Other types of data carriers and associated readers exist, for example magnetic stripes, optical memory tags, and touch memories.
Other types of ADC carriers include RFID tags that may store data in a wirelessly accessible memory, and may include a discrete power source (i.e., an active RFID tag), or may rely on power derived from an interrogation signal (i.e., a passive RFID tag). RFID readers typically emit a radio frequency (RF) interrogation signal that causes the RFID tag to respond with a return RF signal encoding the data stored in the memory.
Identification of an RFID tag generally depends on RF energy produced by a reader or interrogator arriving at the RFID tag and returning to the reader. Multiple protocols exist for use with RFID tags. These protocols may specify, among other things, particular frequency ranges, frequency channels, modulation schemes, security schemes, and data formats.
Many ADC systems that use RFID tags employ an RFID reader in communication with one or more host computing systems that act as central depositories to store and/or process and/or share data collected by the RFID reader. In many applications, wireless communications is provided between the RFID reader and the host computing system. Wireless communications allow the RFID reader to be mobile, may lower the cost associated with installation of an ADC system, and permit flexibility in reorganizing a facility, for example a warehouse.
RFID tags typically include a semiconductor device having the memory, circuitry, and one or more conductive traces that form an antenna. Typically, RFID tags act as transponders, providing information stored in the memory in response to the RF interrogation signal received at the antenna from the reader or other interrogator. Some RFID tags include security measures, such as passwords and/or encryption. Many RFID tags also permit information to be written or stored in the memory via an RF signal.
RFID tags are generally used to provide information about the specific objects on which the RFID tags are attached. For example, RFID tags may store data that provide the identification and description of products and goods, the identity of an animal or an individual, or other information pertaining to the objects on which the RFID tags are attached.
Problems may occur when a plurality of RFID tags are attached to a corresponding plurality of objects that are located in relatively close proximity to each other, and it is necessary to select a particular object of interest among the plurality of objects. Since the object of interest may be similar or identical in visual appearance to the other objects in the plurality, it can be difficult for a user of the RFID reader to readily locate the object of interest, even if the RFID reader has successfully interrogated the specific RFID tag attached to the object of interest—the user simply sees a cluster of similar or identical objects and cannot readily differentiate the object of interest (that had the appropriately responsive RFID tag) from the other objects.
Some semi-automated or fully automated techniques are available to assist the user in locating an object of interest. Such techniques can be performed with some degree of automation using the appropriate instrumentation and algorithms in RFID readers and/or other devices. Such techniques may also be performed manually.
As an example, a known technique to identify the location of an object is through triangulation. With one triangulation technique, the relative position of two or more points of reference is calculated based on two vertices of a triangle (e.g., two angles of the triangle at the points of reference) and the measurable length of a side of the triangle (e.g., a baseline or base of the triangle) between the two vertices. The object of interest is at a third vertex/point of the triangle, and can be located using geometric formulas.
In another triangulation technique, one angle of a triangle and the distance between two points (e.g., a distance between a vertex of the triangle forming a point of reference and the object of interest) are used. Again, geometric formulas can then be used to obtain the location of the object of interest.
Still another technique (for identifying a location of an object of interest) is based on the identification of the intersection point of three circles having diameters equal to distances between points of reference and the object of interest. Geometric formulas are used to obtain the location of the object of interest.
Another technique for identifying the location of object of interest is based on the employment of spatially distributed antennas (for example, an array of antennas) receiving signals from the object of interest. The differences in distances between different antennas and the object of interest would result in phase shifts of receiving signals in said antennas. Applying simple formulas, one skilled in the art can calculate actual differences in distances between the object of interest and each antenna and can determine the location of the object of interest using above described triangulation technique(s).
The various techniques discussed above (whether manual or having some degree of automation) suffer a number of drawbacks. For instance, the instrumentation used for automatically calculating angles and distances can be imprecise in their results. With manual techniques for identifying the location of the object of interest, the user often has to “guess” the location or otherwise search (visually or manually) in the general area where the object of interest may be located, which may perhaps require re-interrogating the general area again in an effort to identify the object of interest. This imprecision and guesswork/searching is inefficient.